Fluxional molecules are molecules that undergo dynamics such that some or all of their atoms interchange between symmetry-inequivalent positions.
Metallocene polymerization catalysts showing fluxional ligand behavior are known. For example, in U.S. Pat. Nos. 6,160,064; 6,559,262; and 6,960,550, unbridged metallocenes have two 2-arylindenyl ligands, each substituted on the 1-position. These propylene polymerization catalysts which can be substituted on the 1-postion by a substituted or unsubstituted alky, alkylsilyl, or aryl substituent produce blocky polypropylene by virtue of rotation about the metal-ligand on a timescale competitive with the formation of polymer chain blocks.
An example of another propylene polymerization catalyst having rotational isomers which can be “frozen out” at lower temperature, is provided in an article to Bercaw et al, in Organometallics, 2012, vol. 31, pg. 1965. The catalyst employed was a “non-metallocene” catalyst having a tridentate ligand set.
The use of phosphinimine catalysts for the solution phase production of ethylene copolymers is well known. See for example, U.S. Pat. Nos. 6,372,864; 6,777,509; and U.S. Pat. No. 6,984,695. Phosphinimine catalysts however, have not previously been known for temperature dependent rotational behavior within a phosphinimine ligand.